1. Field of the Invention
The present invention is related to a semiconductor device and a method for fabricating a semiconductor device and is related to, for example, a semiconductor device having a contact plug for connecting a device portion and a copper (Cu) wire arranged therein and a method for fabricating such a semiconductor device.
2. Related Art
In recent years, new micro-processing technologies have been developed with higher integration and higher large-scale integrated (LSI) circuit performance. In particular, the recent trend is to replace aluminum (Al) alloys with low-resistance copper (Cu) or Cu alloys (hereinafter, referred to collectively as “Cu”) as wire materials to achieve higher LSI performance. Thus, with the aforementioned finer patterns of semiconductor integrated circuits in recent years, a contact hole to connect a Cu wire and a substrate diffusion layer and that to connect a Cu wire and a gate electrode of a transistor have a smaller diameter. Accordingly, the contact holes have an increasingly higher aspect ratio. While aluminum (Al) or tungsten (W) is conventionally used for a contact plug formed in a semiconductor device with a fine structure, application of Cu having lower resistance than W as a contact plug material is being considered to meet the demand for further reduced plug resistance.
One problem that arises here is the occurrence of a junction leak (J/L) by Cu being diffused to a semiconductor substrate. To prevent the junction leak, a barrier layer is formed between a contact plug material and a semiconductor substrate. Here, if Al is used as a contact plug material, a two-layer barrier metal film is formed by forming a TiN film whose crystal orientation is (100) on a semiconductor substrate and then forming TiN, whose crystal orientation (111) has high reliability with Al on the TiN film in the (100) orientation, and it is disclosed in patent documents (see Published Unexamined Japanese Patent Application No. H07-201779, for example).
On the other hand, tantalum (Ta) or tantalum nitride (TaN) is conventionally used as barrier layer material for a Cu wire used in an upper portion of a contact plug. Thus, if Cu is used as a contact plug material, a barrier metal film of Ta or TaN is one possible candidate. However, while these materials have barrier properties against Cu diffusion, a barrier metal film is formed by a sputter process and, as such, it has difficulty in forming a film at the bottom surface side of a contact hole with a high aspect ratio. If a barrier layer is made thicker to ensure barrier properties, the barrier film formed at a frontage of a contact hole may overhang to close the entrance of the contact hole. Given these conditions, poor embedding is expected when Cu is embedded in a plating process. A method of forming a barrier layer by, for example, a chemical vapor deposition (CVD) method with good step coverage is a known method of solving this problem. For example, materials of a barrier layer that can be formed by the CVD method include titanium nitride (TiN). The overhang problem is solved by applying titanium nitride (TiN) to the barrier layer. However, a problem related to insufficient barrier properties may result, causing J/L by Cu being diffused to a substrate.